test(contract): Add Contract v1 test fixtures

- Add valid fixtures: minimal, typical, maximal
- Add invalid fixtures: missing required, wrong units
- Fixtures used for contract validation and round-trip testing

See tests/fixtures/v1/ for test contract samples.

tests/fixtures/v1/invalid-missing-required.json

@@ -0,0 +1,5 @@
+{
+  "title": "Missing ID",
+  "fetchTime": 1738022400000
+}
+

tests/fixtures/v1/invalid-wrong-units.json

@@ -0,0 +1,7 @@
+{
+  "id": "test-notification-004",
+  "title": "Wrong Time Units",
+  "fetchTime": 1738022400,
+  "scheduledTime": 1738026000
+}
+

tests/fixtures/v1/valid-maximal.json

@@ -0,0 +1,17 @@
+{
+  "id": "test-notification-003",
+  "title": "Complete Notification",
+  "body": "This notification includes all optional fields",
+  "scheduledTime": 1738026000000,
+  "fetchTime": 1738022400000,
+  "mediaUrl": "https://example.com/image.jpg",
+  "ttlSeconds": 7200,
+  "dedupeKey": "unique-key-123",
+  "priority": "high",
+  "metadata": {
+    "source": "test",
+    "category": "daily",
+    "tags": ["important", "daily"]
+  }
+}
+

tests/fixtures/v1/valid-minimal.json

@@ -0,0 +1,6 @@
+{
+  "id": "test-notification-001",
+  "title": "Test Notification",
+  "fetchTime": 1738022400000
+}
+

tests/fixtures/v1/valid-typical.json

@@ -0,0 +1,11 @@
+{
+  "id": "test-notification-002",
+  "title": "Daily Update",
+  "body": "Your daily notification is ready",
+  "scheduledTime": 1738026000000,
+  "fetchTime": 1738022400000,
+  "mediaUrl": "https://example.com/image.jpg",
+  "ttlSeconds": 3600,
+  "priority": "default"
+}
+